Geographicgradients in Diet Affect Population Dynamics of Canada Lynx

Abstract

Geographical gradients in the stability of cyclic populations of herbivores and their predators may relate to the degree of specialization of predators. However, such changes are usually associated with transition from specialist to generalist predator species, rather than from geographical variation in dietary breadth of specialist predators. Canada lynx (Lynx canadensis) and snowshoe hare (Lepus americanus) populations undergo cyclic fluctuations in northern parts of their range, but cycles are either greatly attenuated or lost altogether in the southern boreal forest where prey diversity is higher. We tested the influence of prey specialization on population cycles by measuring the stable carbon and nitrogen isotope ratios in lynx and their prey, estimating the contribution of hares to lynx diet across their range, and correlating this degree of specialization to the strength of their population cycles. Hares dominated the lynx diet across their range, but specialization on hares decreased in southern and western populations. The degree of specialization correlated with cyclic signal strength indicated by spectral analysis of lynx harvest data, but overall variability of lynx harvest (the standard deviation of natural-log-transformed harvest numbers) did not change significantly with dietary specialization. Thus, as alternative prey became more important in the lynx diet, the fluctuations became decoupled from a regular cycle but did not become less variable. Our results support the hypothesis that alternative prey decrease population cycle regularity but emphasize that such changes may be driven by dietary shifts among dominant specialist predators rather than exclusively through changes in the predator community.

Theoretical impacts of habitat loss and generalist predation on predator–prey cycles

“…To produce limit cycles remotely comparable to the Kluane cycles, the maximum generalist predation rate for the May model needs to be close to the lower bound of the Kluane estimate (0.1 prey/ha/year), and the R-M model requires a rate below the mid-range value (1.0 prey/ha/year). One possible explanation is that this estimate includes removals from predators who function as specialists in Canada and actually cycle along with snowshoe hares (O'Donoghue et al 1997, Rohner et al 2001, Roth et al 2007. In this case, the upper bound for the maximum generalist predation rate is likely lower.…”

The influence of coyote on Canada lynx populations assessed at two different spatial scales

“…As the period of lynx cycles is about 10 years (e.g. Roth et al 2007), we only estimated the periodograms for periods ranging from 5 to 15 years. Statistical significance of the highest peak (corresponding to the dominant harmonic) was used as a formal test of cyclicity (Glynn et al 2006; we used α = 0.05).…”

“…Statistical significance of the highest peak (corresponding to the dominant harmonic) was used as a formal test of cyclicity (Glynn et al 2006; we used α = 0.05). We also used the height of the highest peak, or spectral power, as a measure of the intensity of cyclicity, independently of whether it reached significance or not (Roth et al 2007). The oscillatory period at peak was also computed and called "T_cycle".…”

“…Strongly cyclic dynamics of the lynx in the boreal zone is attributed to its high degree of specialization on snowshoe hare ('diet specialization' hypothesis: Roth et al 2007). Gradual loss of lynx cyclic dynamics towards the south end of its range is currently explained by the emergence of additional trophic interactions.…”

“…Gradual loss of lynx cyclic dynamics towards the south end of its range is currently explained by the emergence of additional trophic interactions. First, this phenomenon is observed through apparent reduction in specialization of the lynx on snowshoe hare, attributed to the higher availability of alternative prey the lynx can switch to during periods of hare scarcity (Roth et al 2007). Second, concurrently with loss of lynx cyclic dynamics, the apparent loss of truly cyclic snowshoe hare dynamics towards the south of the hare's range (Smith 1983) is potentially mediated by an increase in the number of generalist predators with which lynx may compete directly (Murray 2000 and references therein, Ripple et al 2011).…”